Question: Simplify the following expression: $z = \dfrac{a^2 - 12a + 20}{a - 2} $
First factor the polynomial in the numerator. $ a^2 - 12a + 20 = (a - 2)(a - 10) $ So we can rewrite the expression as: $z = \dfrac{(a - 2)(a - 10)}{a - 2} $ We can divide the numerator and denominator by $(a - 2)$ on condition that $a \neq 2$ Therefore $z = a - 10; a \neq 2$